The present invention relates to a host controller.
In recent years, the Universal Serial Bus (USB) standard has attracted attention as an interface standard for connecting a personal computer with a peripheral device (electronic instrument in a broad sense). The USB standard has advantages in that peripheral devices such as a mouse, keyboard, and printer, which have been connected using connectors of different standards, can be connected using connectors of the same standard, and so-called plug & play and hot plug can be realized.
On the other hand, the USB standard has a problem in which the transfer rate is lower than that of the IEEE 1394 standard which has also attracted attention as the serial bus interface standard.
The USB 2.0 standard has been developed and has attracted attention. This standard realizes a data transfer rate of 480 Mbps (High Speed (HS) mode) remarkably higher than that of the USB 1.1 standard while maintaining compatibility with the USB 1.1 standard. The USB 2.0 Transceiver Macrocell Interface (UTMI) standard has also been developed. This standard defines the interface specification of the physical layer circuit and the logical layer circuit of the USB 2.0 standard.
In the USB 2.0 standard, a transfer mode called the HS mode is provided in addition to the Full Speed (FS) mode which has been defined by the USB 1.1 standard. In the HS mode, since data is transferred at a transfer rate of 480 Mbps, data transfer remarkably higher than that of the FS mode (12 Mbps) can be realized. Therefore, the USB 2.0 standard can provide an interface suitable for storage devices such as hard disk drives and optical disk drives for which a high transfer rate is demanded.
In the USB 2.0 standard, small-amplitude signals are transferred at a high speed in comparison with the USB 1.1 standard. Such high-frequency small-amplitude signals are affected to a large extent by the quality of the transmission line and the termination resistor of the device. Therefore, a USB 2.0 host controller must be provided with a disconnection detection circuit which can accurately detect that the host and the device have been disconnected for such small-amplitude signals which tend to be affected.
JP-A-2002-232273 discloses a window voltage comparator for determining whether the difference between the voltages of the differential signal lines is greater or smaller than a set value. JP-A-2002-344540 discloses providing a squelch circuit which detects the presence or absence of a pair of differential reception signals and detecting disconnection using the voltage level of one of the differential signals.